Factors influencing the infant gut microbiome at age 3-6 months: Findings from the ethnically diverse Vitamin D Antenatal Asthma Reduction Trial (VDAART)

In the gut, there are millions of bacteria and other micro-organisms, collectively called the gut microbiome.  Microbes in the gut are known to be important modulators of the developing immune system.   In this month’s issue of JACI, Sordillo and colleagues look at predictors of the gut microbiome in infancy (J Allergy Clin Immunol 2017; 139(2): 482-491).  Microbes present in this early life window may ultimately affect the risk of allergic disease later in childhood. 

They looked at stool samples in over 300 infants born to mothers in the Vitamin D Antenatal Asthma Reduction Trial (VDAART), a trial in which pregnant women took vitamin D to see how it would impact their children’s health.  In the stool, they looked at the bacterial genes to see what bacteria were present.

They found that race, mode of delivery, and formula-feeding are associated with different composition of gut bacteria.  Black race and caesarean section were independent predictors of having lower levels of Bacteroides.  This is important because lower Bacteroides abundance has already been associated with immune changes predisposing to asthma and allergic disease.  In addition, formula feeding was linked to higher levels of Clostridia.  Previous studies have suggested a link between Clostridia and development of atopic dermatitis, wheezing and allergic sensitization.

This study points out that factors with the potential to increase allergic disease risk are also associated with alterations in the infant gut microbiome, but there are still a lot of unanswered questions.  Do these factors (race, mode of delivery, formula feeding) act via changes in the infant gut microbiome to increase allergic disease risk?  Do these changes in the gut microbiome persist through childhood?  Can breastfeeding change the microbiome and reduce the risk of allergic disease?  Finally, can we figure out which species and subspecies are most closely associated with these risks?  Further research is needed, but this study provides a meaningful step towards providing answers.